When asked, Cohen said the U.S. is not intentionally looking the other way while Iran exceeds the export quota.
"We're not, and what I would say though is let's let the process run its course here," he said. "We are in the beginning of June. We still have more time on the clock here with the Joint Plan of Action, and we'll watch to see how things develop."
The sanctions program against Iran required a broad international agreement to cut off purchases of Iran's oil, but six countries were given waivers: Taiwan, Turkey, South Korea, Japan, India and China.
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The exceptions were designed to give those nations time to find other supplies, but every six months they were to show that they were buying less crude from Iran. The program worked, and Iranian exports dropped from 2.7 million barrels per day to less than a million in 2013. The sanctions are widely credited with bringing Iran to the negotiating table last year.
But data show most of those countries are now importing more than they did last year; China, in particular, has been buying much more. According to Energy Aspects, Chinese imports from Iran spiked to a record high of 800,000 barrels per day in April. The previous high stood at around 650,000 barrels per day.
In a note to clients, Energy Aspects' chief oil analyst Amrita Sen wrote that the number "highlights the limited importance placed by China on the conditions of the U.S. sanctions waivers."